Electric circuit breaker



June 13, 1939. D. c. PRlNCE ELECTRIC CIRCUIT, BREAKER Filed June 6, 1935 Flgl.

2 Sheets-Sheet l Inventor: David C. Prince June 13, 1939. D. c. PRINCE ELECTRIC CIRCUIT BREAKER Filed June 6, 1935 2 Sheets-Sheet 2 Patented June l3, 1939 UNITED STATES 2,102,588 nmc'mrc cmcm'r BREAKER David C. I Prince,

Swarthmore, 1a., assignor to -General Electric Company, a corporation of New York Application June 6. 1935. Serial No. 25,267

- '18 Claims. My-invention relates to electric circuit break-'- ers for interrupting high tension power circuits.

Circuit breakers of the impulse type for example wherein a jet of oil or -other suitable arcextinguishing liquid is projected by a piston, or anequivalent source of pressure, across the are formed upon opening of the circuit have'proved eflective in quickly and positively interrupting high tension, alternating current power circuits. The amount of oil or arc-extinguishing liquid required for a.v single interrupting operation in this type of breaker is quite small as compared with the conventional tank type oil circuit breaker. Furthermore, the insulating and arcextinguishing characteristics of'the oil used in a circuit interruption are affected to a relatively slight extent. Accordingly, this type of breaker has distinct advantages in that the low oil content 1 for example results in reduction of cost of maintenance,

breaker.

In applying this type of breaker to circuits operating at unusually high voltages, such as 287 kv.,. certain problems in design and operation are encountered, and it is an object of my invention inovercoming these problems to provide 'an improved, high tension, circuit breaker whichshall have unusually high interrupting speed throughout the entire interrupting range.

A further object of my invention is the provision of a circuit breaker of the aforesaid type wherein normal operation results in uniform use of and inappreciable deterioration or decrease in insulating value'of the oil or other arc-extinzm guishing liquid. J

A further object of my invention is the provision 'of an impulse type circuit breaker which is of rugged construction and adapted to withstam; severe shock, such as earthquake-for ex- 49 ample, without damage.

My invention will be more fully set forth in the following description referring to the accompanying drawings, and the featuresv of novelty whichcharacterize my invention will be pointed 45 out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawings, Fig. 1 is an elevational view of the main portion of an electric circuit breaker embodying my invention; Fig. 2

m is an elevationalview, partlyin' section, of one of the interrupting units of the circuit breaker shown by Fig. 1; Fig. 3 is a plan view; partly in section, of contact structure and assodated apparatus shown in Fig. 2; Figs. 4 and 5 are sec- ..55 tional andperspective respectively, of

fire hazard, and size of the circuit and climate, an outer insuiati to a retaining member II.

contact and baiiie structure shown by Fig; 3; and Fig. 6 is an elevational view of the breaker shown in Fig. 1 provided with electrostatic shielding means. I

Referring to Fig.- 1, there is illustrated a high 5 tension, multiple-break electric circuit breaker of the impulse type comprising a pair of similar interrupting units I and 2 for interrupting a a high tension power circuit indicated at 3. The units are connected in series in the circuit 3. 10 Each interru ting unit is pivotally mounted at I on a stationary insulating support 5, the free terminal ends 3' of the interrupting units having a nonrigidv connection with the insulating supports 6. v v

The operating means for both interrupting units includes an operating rod 1 which extends upwards from operating mechanism (not shown) through the hollow insulating support 5 and term'inates in linkage coacting with the interrupting units. The insulating supports 5 and 8 together with the operating mechanism above referred to are suitably 'mounted on structural steel framework or other rigid foundation (not shown).

Referring more particularly to Fig. 2, the interrupting unit 2. which is generally similar in all respects'to the'interrupting unit I, comprises a metallic supporting housing 3 which is carried at the pivot 4., To this housing is secured an elongated insulating casing 9 comprising a-cy1in-. drical tube of mechanically strong insulating material; such as fibre. The tube 0 is clamped at Ill to an annular flange of the casing I and is in communication with the interior of said casing. The opposite end of said tube is provided'with a terminal capll whiclbforms with the tube 9 and casing 8 a reservoir for a suitable arc-extinguishing liquid, such as oil, for example.

In order to insulate the apparatus more effectively. for high voltages and for protecting the 40 interrupting unit from the eflects of weather ng casing is provided, comprising in the present instance a pair of insulating shells l2 and ll of ceramic material .suitably united at adjacent ends by a flexible connection, such as a metallic bellows II, for

.' example; The insulating shell I! is suitably connected at one end at I! to an annular flange i8 7 of the casing I, and the free'orterminal end or the insulating shell I! is suitably connected at 11 a The retaining member II is securedin turn by a ring-wedge device at II tothe corresponding end of the insulating tube Sand the end cap II is secured and sealed at II to the retaining member. Accordingly, the I strong fibre tube 9, rather than the outer ceramic casing, is subjected to the stresses incident to operation and accidental shock.

The annular space 2| between thetube 9-and shells l2 and I3 is sealed with respect to the interior of the tube 9 and is filled with insulating liquid, such as oil.

The oil space is filled from an oil reservoir 2| formed by the casing 8. Accordingly, accidental breakage of one of the insulating shells would permit escape only of the oil in the space 2|, and would not interfere with normal operation of the interrupting unit. Furthermore, since the oil in space 2| is sealed with respect to the oil in tube 9, except for an interconnecting vent in the casing cover 8'f, a different in-. sulating liquid of suitable characteristics may be used'where desired between the fibre supportin tubes and ceramic insulators.

It shall be' understood that any suitable insulating liquid may be used and that the term oil as used herein is intended to comprehend both insulating and arc-extinguishing liquids.

The mounting for the' interrupting unit comprises at one end the pivotal support 4 to which the casing 8 is directly connected, and at the other end a roller 22 carried' by a bracket 22'. The roller engages a flat bearing plate 23 on the support 6, thereby providing a nonrigid and sliding connection between the free end of the unit 2 and the insulating support 6. This arrangement not only provides for limited longitudinal or transverse movement of the interrupting unit relative to the support 5, such as due to temperature variations and uneven foundation settling, butalso insures against damage due to shock, such as earthquake, for example.

circuit interruption. 1r desired, a materialfor absorbing moisture, such as silica gel, may be used at the vent pipe for preventing accumulationof moisture in the breaker.

The circuit interrupting means comprises a plurality of pairs of contacts 34-35, 36-31,

38-49, and 49- connected in series and arranged generally along the longitudinal axis of the insulating tube 9. The contacts are mounted on and supported by an insulating partition 42 likewise extending longitudinally of the tube and arranged to'form upper and lower chambers 9' and 9" therein. For the purpose of providing a more effective seal between the partition and casing wall, sealing flaps 42' of suitable' material such as leather are secured at the lateral edges "of the partition.

' The partition 42 is connected to a positioning or bracing member 43 through a plurality of links 44 forming with the partition a structural contact unit which can be inserted during assembly through'the free or outer end of the tube 9.

The supports 5 and 6 each comprise an inner cylindrical member 24 of strong insulating material, as in the case of the tube 9, for supporting the central and terminal ends of the interrupting units. is resiliently connected at 26 with respect to the insulating cylinder 24, serves only as additional insulating and protective sheathing. The space between the cylinders and shells is preferably filledwith a suitable insulating liquid.

For the purpose of providing flexibility between the operating means and'the interrupting units the interconnecting mechanism is housed in relatively movable interconnected, casings. The operating rod 1 extending through the central insulating support 5 is connected through a link 26 to'a. contact operating lever 2l at 29 which extends through. a wall of the casin 3, as illustrated, and'is pivotally mounted at 28 within the casing. The operating rod 1 is guided within an extension casing 30 which isprovided with a T-connection at 3| for enclosing the connection between the operating rod and the operating levers 21 of both interrupting units,- The T-connection includes a sleevemember 32 extending through a wall of the casing 8 and having a sliding liquid-tight seal therewith at 33. Accordingly, a limited movement of the interrupting unit 2 about its pivotal support 4 is permitted without lossor. throw of oil from the arrangement insures sumcient flexibility in the The outer insulating shell 25, which the retaining member tube the member 43, as best shown by Figs. 2 and 4, is moved longitudinally with'respect to the partition in a direction tending to straighten in toggle fashion the links 44. This movement and positioning of member 43 is suitably accomnuts at 45 coacting with l'l. Since the member 43 bears against the lower wall of the tube 9, the thrust exerted by the links 44 firmly braces the partition 42 against the opposite walls of the tube. This arrangement is clearly illustrated by Fig. 4 wherein the partition 42 is shown pressed plished by adjusting by the members 43 and 44 against the upper wall of the tube 9 to form upper and lower chammovable contact 35, 31, 39, and 4|. being connected by means of a cross-piece oryoke 46 to a pair of rods 41. which are mounted on rollers structure is il-- lustrated more particularly by Figs. 3 and 5, each 48 for reciprocal longitudinal movement with re- .spect to the coacting stationary contacts. The movable contactis provided with a guide stem as at 35' whichtis guided for reciprocal movement in the yoke 46. A resilient connection, such as spring 46, is provided between the yoke and contact, the yoke engaging a shoulder at 35," on the contact'stem for separating the cont'acts.

The movable and stationary contacts. of adjacent pairs of'contacts are electrically connected by flexible conductors 49; thereby connecting the respective pairs of contacts in series. Each stationary contact (Fig. 3) is rigidly mounted in an insulating member 59 depending-from the rartition 42. -As illustrated by Fig. 5, the member circuit breaker 'housingand mechariism'struc- 'ture for compensating comparatively severe stress and shock, suchas above described. The housings 3 both vent 'into the T-housing 3 l which is provided with suitable means, such as a vent pipe 3| for the removal of gas formed 5!] likewise provides bearings for the rod guiding and supporting rollers 18.

The stationary contact structure includes a conducting block 34 to which the contact 3| is secured, and a conductor stud 346 which con-- nects the block 3441 to the casing 8 at 34c (Fig.2) The stationary contact of each unit nearest the casing 3 is therefore electrically connected thereto, the casings 8 being electrically connected in any suitable manner, such as by a' flexible con ductor -(not shown).- Also, the movable contact at the free end of each unit is electrically connected bya flexible conductor I l' to the terminal cap ll. 7

In circuitbreakers of this type, arc interrup- 7 tion is efiec'teifby a jet of liquid across the arc,

the jet passage generally being transversely oi the arc. The partition 42 is provided in the present instance with a pair-of openings forming jet or exhaust passages and 52 from the lower chamher 9'', which is filled with arc-extinguishing liquid, to the upper chamber 9', which is but partly filled as indicated by the oil level. A suitable number of exhaust passages are spaced along the arc path between the contacts as best illustrated by Figs. 3 and 5. Accordingly, when the liquid in the lower chamber is placed under pressure as hereinafter described during opening of the circuit,- two jets of oil pass transversely through the arc path to exhaust into the upper chamber through the openings 5| and 52.

For the purpose of'completely separating the as illustrated. so as to exhaust at opposite sides of the baffie 53, thereby effectively preventing restriking of the arc beyond the baflle structure; It will of course be apparent that a plurality of pairs of oil passages may be provided so as to exhaust in staggered relat on at opposite sides of the baille. i

The stationary and movable contacts abut in the closed circuit position. as illustrated by Fig. 3. the point of contact being nearly opposite one of the exhaust passages.

proximity to the exhaust passa es 5| and 52. the contacts are provided withofi'set portions 34 for maintaining the are at the upper part of the c ntact as illustrated by Fig. 5. Accordin ly. flow of arc-extinguishing l quid under pressure from the lower-chamber across the arc path and throu h the exhaust assage is more effective to extin uish the arc-than in the case where the are root is at the lower peri hery-of the c n a The source of res i'i e for d v ng the o l fr m.

the lower chamber throu hthe .arcs into the upper chamber in accordance with the circuit o ening operation c mprises in the present instance a p ston 56 operable in'an open end cy inder '51 formed in the oasine R. It shall be understood that any other suitable source of pressure may be used. Th iston 5k is o erative, ly con ected through a. l nk 58 to the onera ng lever 21 and is provided with valves 5*. which are suitably disposed in the operat ng face of the piston..so astobe firmly sealed'and closed by fluid pressure during the downward or working stroke of the piston and to'open on the return stroke of the piston for passing oil above the piston to the lower reservoir 8. formed in'casing 8.

In view of the fact that the space 9' above the partition 42 is in tree communication with thevalves-to the lower part of the reservoir. A conspace in the casing 8 above the piston, it will-be clear that oil in the upper chamber after each interruption circulates back through the piston tinuous separating wall between the piston and partition 42 is formed by the wall portion 50 and the insulating end wall 5| which is secured to In'order to maintain the are upon separation of the-contacts in close the conductor stud 34b (Fig. 3) and forms a seal between the wall portion 50 and partition 42.

Coacting with the piston is another valve 5|, comprising in the present instance a simple flap valve, pivotally mounted in the casing 8 at 52 and arranged to close the passage 6| betweenthe piston and the lower chamber 9" during the return or suction stroke of the piston. The valve 5| opens freely under fluid pressure on the working stroke of the piston and closes when the pressure in the lower or are chamber 9" exceeds. that in the oil reservoir 8'.

By this arrangement comparatively fresh and clear oil is provided for each interrupting operat on. That is, the oil instead of being sucked back into the lower chamber after an arc-interrupting operation is drawn into the casing 8 where it is directed through the piston to the lower reservoir 8'.- The entire quantity of oil directed across the four breaks during a single interrupting operation is small as compared with the quantity of liquid in the reservoir and lower chamber, as will be observed from the length of the piston stroke. Accordingly, the valves 59 and SI insure practically complete use of the fresh oil supply before re-use of oil discharged into the upper chamber by circuit interrupting operation. Consequently, the rate of oil deterioration due to carbonization and other causes is uniform and hence comparat vely slow.

Another function of the valve 5| is to prevent stickingof air or gas, the dielectric strength of which is considerably less than that of oil or other suitable insulating and arc-extinguishing liquids, into the. lower chamber during the return stroke of the piston. The valve 6| in closing on the suction .stroke of the piston prevents the formation of air or gas pockets adjacent the contact structure which might result were air or gas sucked from the upper chamber through the exhaust ports into the lower chamber. Furthermore. the presence of air or gas, beneath the partition 29 would tend to defer the building up of pressure in the otherwise substantially incom pressible oil and so delay the blast efiect. Also in this connection. the blast effect due to are pressure in the case or large currents. such as short circuit currents. is most efliciently utilized by reason of the valve 5| which closes when the 'arc chamber pressure tends to reverse the piston.

The contact opening and closing mechanism is likewise associated with the operating lever 21 sons to coact with the piston 56. The pair or rods I] on which the four movable contacts are mounted is connected by means of a yoke. or the like ,'at 63 to a link GI initurn connected to one arm of a; bellcrank R5. The crank 85 is p votally overcenterwith respect to pivots 66 and H so as to bias the crank 55 in a clockwise direction, thereby holding'the contacts .in firm engagement.

The operating lever 21 s provided with a pair of cam plates 12 and I3 having cam surfaces 12' .and 13' arrangedto coact with the crank roller Bl. The cam face 13' coacts with the roller 68 in the circuit opening operation and the cam face '12 in theclosingoperation. When the operating rod I is lowered, as viewed in Fig. 2, for efiect ing-the interrupting operation, the consequent,'

counterclockwise movement of the lever 21 effects not only the working stroke of the piston 56 for placing the oil in the lower chamber under pressure but also counterclockwise rotation of crank 5 65 for opening the contacts. The cam face 13 is designed so that a comparatively quick contact separation is obtained at the initiation of the circuit opening movement, after which the rate of separation is decreased coincident with the oil f blast across the arcs. The compression spring 10 furthermore, after it has passed its. over-center position, biases the contacts towards the completely open position.

The circuit closing operation is effected by rais- No; 25,222, flied concurrently herewith by Carl, Thumim and assigned to the same assignee as the present invention, and now Patent No. 2,071,185, issued February 16, 1937.

80 In efllciently interrupting a high tension power,

circuit by means of a multiple-break arrangement, it is essential that there be a fair degree of voltage distribution between the separate breaks. That is, in order to realize the advantage of a plurality of breaks means should be provided for preventing concentration .of the voltage at one or two breaks at circuit interruption. This-has been done by connecting grading resistances across the contacts, but this arrangement has obvious disadvantages in actual practice due to burning out of the resistances, added cost. etc.

For thepurpose oi more evenly distributing the voltagebetween the terminals of the interrupting unit, I providemeans for equalizing the electrostatic stresses along the contact path between .the breaker terminals. In one arrangement, re- I I ferring to Fig. 2, a conducting band, comprising in the present instance the metallic bellows connection ll.'is disposed intermediate the terminals of the units so as to encircle the path along which the breaks are disposed. .The electrostatic fleld stresses are thereby more evenly distributed between the terminals with the result that more even voltage distribution at the individual breaks is obtained. It will be understood that a plurality of conducting bands may be used. the number and positioning thereof depending on the particular design and operating requ rements of the breaker.

'In another arrangement, referring to Fig. 6, the terminals of the breaker are provided withmetallic shields i"and 2' which inthe present instance are of cone 'or hood like shape and designed so as to equalize or prevent high concentration of 1 7 P 'Qiierand more even distribution of potential at the points of contact separation in a'multiplebreak high voltage circuit interrupter by means of electrostatic grading.

-It should be further understood that my invention is not limited-to specific details of contrated, andthat changes and modifications may occur to one skilled in the art-without departing from the spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit breaker of the multiple break type comprising a ceramic casing, the longitudinal'axis of which is substantially horizontally positioned, relatively movable contacts. in

said casing and a pair of stationary supports ad jacent the opposite ends of said casing, said casing being. secured for relative movement to one of said supports and provided with a sliding'connection with the other support for permitting sudden movements of the character of earthquake tremors of said supports without fracture of said ceramic casing.

2. An electric circuit breaker comprising a ceramic casing including a circuit-interrupting unit, a stationary support adjacent one end of said casing, operating mechanism at said support coacting with said interrupting unit, said- .struction' and arrangement thereof herein illuscasing including a substantially complete interrupting unit, the longitudinal axis of each casing being substantially horizontally arranged, acentral stationary support on which each casing is pivotally mounted at one end so that the longitudinal axes of said casings are in general alinement, operating mechanism at said support coacting with both of said interrupting units, and a stationary support providing a nonrigid connection at the free end of each of said connect ons.

4. An electric circuit breaker of the impulse type comprising a pair of separate casings. each casing comprising separable contacts. an arc-ex-. tinguishing liquid and a piston for directing liquid between said contacts upon opening of the circuit, a central stationary support, each of said casings being pivotally mounted on said support, operating mechanism mounted with respect to said support coacting with the piston and the contacts in each of said casings notwithstanding variations in relative position of said casings and central support, and a support at the free end of 1 each of said casings providing a nonrigid connection therewith.

5. An electric circuit breaker comprising means forming an arc chamber, relatively movable contacts separable to form an arc in said chamber, an

and are chamber forprecluding reversal of said piston in the'event-that the arc pressurexin said chamber exceeds the piston pressure. f

6. An 'electric circuit breaker comprising means forming an. arc'chamber having an exhaust opening, relatively movable contacts sep- 7. An electric circuit breaker comprising relatively movable contacts, means forming separate chambers, said contacts being separable in one of said chambers, said chambers being interconnected by an opening arranged substantially opposite the point of separation of said contacts, an arc-extinguishing liquid substantially filling thecontact chamber, a source of pressure for effecting flow of a comparatively small portion of said liquid through said opening and between said contacts upon a single separation thereof, and valve means for readmitting said liquid from said last-named chamber to said contact chamber and for progressively using, in accordance with successive circuit opening operations, substantially the complete unused liquid supply in said contactchamber.

8. An electric circuit breaker comprising relatively movable contacts, a partition forming separate chambers, said contacts being separable in one of said chambers, said partition having an opening interconnecting said chambers and arranged substantially opposite the point of separation of said contacts, a supply of arc-extinguishing liquid substantially filling the chamber in which said contacts are disposed, a piston for expelling a quantity of liquid from said supply chamber through said opening into the' other chamber and between said contacts upon separation thereof, and valve means adapted to open in accordance with a return stroke of said piston for readmitting said quantity of liquid 'to said supply chamber at a point remote with respect to said partition opening.

A 9. An electric circuit breaker of the impulse- .type comprising relatively movable contacts, 'a partition forming two chambers in one of which said contacts are disposed, said contact chamber likewise containing an arcextinguishing liquid, said partition having an opening interconnecting said chambers substantially opposite the point of separation of said contacts, a piston for expelling from said contact chamber a'quantity of said liquid through said opening in accordance with a circuit opening operation, and a valve controlling communication between said contact chamber and said piston, said valve arranged to close during the return strokepf said piston.

10. An electric circuit type comprising relatively movable contacts, a partition forming two chambers in; one 01 which said contacts are disposed, said contact chamber likewise containing a supply Marc-extinguishing liquid, said partition having an opening interconnecting said chambers and disposed tially opposite 'the point of separation of said contacts, apiston in communication with said liquid for expelling a quantity of liquid through said opening into the other chamber in accordance with separation .of said contacts, valve means associated with said piston for re-admitting? saidquantity of liquid to said supply cham-v breaker or. .the impin e."

accordance with the return stroke of said piston,

and a valve controlling communication between said supply chamber and said piston arranged to closeso as to prevent drawing of air into said supply chamber during the return stroke of said piston.

11. An electric circuit interrupter comprising means forming an arc upon opening of the circuit, insulating baiile structure having a plurality of passages, the entrances of said passages being spaced along the path of said are and the exhausts of said passages bein'g similarly spaced along said pathand extending in diverging directions at opposite sides of said baflle structure, and means for directing an arc-extinguishing liquid across said are and through said passages.

12. An electric circuit breaker comprising relatively movable contacts, a casing forming a chamber in which said contacts are disposed, an arc-extinguishing liquid in saidchamber, means forming a plurality of passages leading from said chamber, the entrances of said passages disposed adjacent and in substantial alinement with the arc path formed upon separation of said contacts, a source of pressure for directing liquid from said chamber across said arc path to exhaust through said passages, and a baiile extending longitudinally of said are path between said passages so as to separate the exhausts therefrom.

13. A high tension multiple-break circuit breaker comprising an elongated casing, a pinrality of pairs of contacts connected in series spaced along the longitudinal axis of said casing, said casing having a partition forming two chambers in one of which said contacts are disposed, an arc-extinguishing liquid in said contact chamber, said partition having a plurality of exhaust openings adjarent each pair of contacts and spaced longitudinally of the arc path formed upon separation of said contacts, a source of pressure for directing liquid from saidcontact chamber through each arc path and associated exhaust openings into the other chamber upon opening of the circuit, and a baille in said other chamber extending longitudinally of said casing and forming with said partition casing 'separate enclosures, said exhaust openings arranged in staggered relation to vent at opposite sides of said bailie. I q

14. An electric circuit breaker comprising relatively movable contacts, means forminga chamber in which said contacts operate," an arc-extinguishing liquid in said ,chamber, said chamber being provided with a pair of. exhaust passages, the entrances of said passages being disposed adjacent and in general alinement with the arc path formed upon separation of said contacts, a source of pressure for directing liquid from said vchamber across the arc path into said passages,

said passagesexhausting in diverging directions,

'and a baliie the longitudinal axis of which is generally parallel to said are path disposed between tlie. exhaust openings of said passages for completely separating the exhausts therefrom.

'15. An electric circuitbreaker comprising relatively movable contacts, means forming a chamher in which said contacts are disposed, an arc- Y extinguishing liquid in said chamber, said chamber having-an 1exhaust opening substantially opposite the arc patli formed upon separation of said contacts, said contacts having coacting raised portions at points nearest said exhaust I opening ,i'or retaining the are near said opening, ber after a circuit opening operation and in said chamber across said arc and through said exhaust opening in accordance with separation of said contacts.

16. An electric circuit breaker comprising an elongated casing, a structural unit including relatively movable contact structure arranged to be removably mounted in said casing, relatively movable means connected to said unit and adapted to engage a wall of said casing, said means being movable to a nonobstructing position when said unit is placed in saidcasing, and

ed' to be placed in position through one end of said tube, and means for adjusting said member relative to said partition so as to force by means 7 of said links said member and said partition into engagement with opposite walls of said tube.

18. An electric circuit breaker comprising 5 means forming an arc chamber having an exhaust opening, relatively movable contacts separable within said chamber substantially opposite said opening, a supply.- of arc-extinguishing liquid, part of which is in said chamber, means 10 for creating pressure in said chamber for expelling some of said liquid from said chamber through said exhaust. opening upon separation of said contacts for extinguishing arcing, means separate from said are chamber for returning 1 said exhaust liquid to said supply so that said exhaust liquid is used again only after substantiallycomplete use of the unused supply, and valve-means for controlling said liquid return in accordance with operation of said pressure- 90 creating means.

DAVID C. PRINCE.

CERTIFICATE OF coaREcTIoN.

Patent no. 2462,5863.

June 5, 959.-

'DAVID c. PRINCE.

It is hereby certified that error appears in the printed specification of the above mnnber ed patent requiring correction as follows: Page 2, second column, line 38, after the word and period "therein." insert'the following sentence a The contact unit is readily withdrawn through the outer end of tube 9by moving themember J 5 in'a horizontal direction (tothe right as viewedinFig. 2) so that the toggle at L l; collapses and the partition I 2 drops away from its braced position. and that the said Letters Patent should be read with this correction there'-' in that the same conform to the record of the case inthe Patent Office.

Signed and sealed this 8th dayof August, A. b.1959. I

(selifi Leslie Frazer, Acting Commissioner of Patents. 

